How tinplate is made

A tin can is steel wearing a thin coat of tin, plated onto a strip moving along a line.

stations: 6
things upstream: 27
raw sources: 13
steps from the ground: 5

The short version

Tinplate is thin steel sheet with a coating of tin that keeps it from rusting. The steel is rolled into a thin strip, pickled in acid to remove scale, rolled again cold, annealed, and then plated with tin, now usually by electric current. The strip is then cut into sheets or coiled for can makers.

Roll the steel thin

Low-carbon steel is rolled in a strip mill into a long band. Early hot strip mills could not make strip suitable for tinplate, so the thin gauge came later from cold rolling.

Goes in
Steel
Pickle away the oxide

The strip runs through acid to remove mill scale. Tin only sticks properly to bare, clean steel.
Cold-roll it again

From 1929, cold rolling was used to reduce the strip to its final thin gauge. The surface comes out smooth and bright, which makes a good base for plating.
Anneal to soften it

Cold rolling hardens the steel, so it is heated again to make it soft enough to be drawn and folded into a can. Older pack mills annealed plates for 10 to 14 hours.
Plate it with tin

The strip is covered with a thin layer of tin. Old mills dipped plates in pots of molten tin under a flux. Modern lines use continuous electrolytic tinning, where electric current builds the tin layer on the moving strip.

Goes in
Tin
Cut or coil it

At the end of the line the strip is cut with a guillotine shear into sheets or wound into a coil and sent to a can maker.

End of the lineTinplate Next it goes into tin can, canned tuna, air freshener and 1 more.

Worth repeating

The first strip mill for tinplate was built at Ashland, Kentucky, in 1923.
Old trade sheets measured 20 by 14 inches and were packed 112 to a box that weighed about 51 kilograms.